Field of the Invention
The present invention relates to a pneumatic tire.
Description of the Related Art
Conventionally, with respect to pneumatic tires, there has been adopted a technique where cuts referred to as sipes are formed in blocks formed on a tread portion, and a traction performance (braking performance) on a road surface having a low friction coefficient such as an icy road surface is improved by an edge effect of the sipes.
On a road surface having a low friction coefficient, a ground contact pressure in a center region of the block is higher than a ground contact pressure in a peripheral region surrounding the center region. Accordingly, the ground contact pressure becomes non-uniform among the respective portions of the block thus deteriorating the ground contact property of the whole block. Because of such deterioration of the ground contact property of the block, a braking performance of the pneumatic tire on an icy road surface is deteriorated.
JP-A-2011-11695 and JP-A-1-47603 propose techniques where a plurality of sipes which extend radially from a center portion of a block are arranged on the block, and a recessed portion which communicates with the plurality of sipes is formed at the radial center of the sipes. In such a pneumatic tire, by arranging the sipes and the recessed portion on the center portion of the block, a ground contact pressure of the block can be made uniform between a center region and a peripheral region and hence, a braking performance of the pneumatic tire on an icy road surface can be improved.
However, in the pneumatic tires described in JP-A-2011-11695 and JP-A-1-47603, the plurality of sipes extending radially from the center portion of the block and the recessed portion arranged at the radial center of the sipes communicate with each other and hence, the center portion of the block is liable to fall. Accordingly, there arise drawbacks such as the occurrence of chipping of rubber at a connecting portion between the sipes and the recessed portion, the occurrence of crack initiating from an outer side edge of the sipe in the radial direction and nipping a foreign substance such as a small pebble in the recessed portion.